答案:[解析]这是虚拟语气在条件状语从句中的应用。从句是省略if的条件状语从句,用过去完成时“had known”表示对过去的假设,主句要选择“would have done”结构,故选B。2010年12月英语三级(A)考试模拟题(语法词汇篇5)Directions: In this section, there are 10 incomplete sentences. You are required to complete each one by deciding on the most appropriate word or words from the 4 choices marked A), B), C) and D).Then you should mark the corresponding letter on the Answer Sheet with a single line through the center.For your entertainmentTo help you enjoy your trip, we provide a range of newspapers. On our MD-11 and Boeing aircraft, we provide music and video programs. On Airbus A 321/320/319, short videos are shown.Meals and drinksDuring most flights we serve you a tasty meal and drinks. Beer, wine and other drinks are served free of charge. Coffee, tea and juice are served free of charge on all domestic (国内的) flights. On domestic flights leaving before nine and on all flights to Northern China, a snack is served.Eastern Flight ServiceSafety and convenience1) Seat belts: remain -46- while the “Fasten seatbelts” sign is on2) Smoking: not allowed on board3) Mobile phones: used only when the airplane is -47-4) CD and DVD: not allowed to play -48-Entertainment provided1) newspapers